I. Field of the Invention
The present invention relates to a telescopic tube for electric household appliances. In particular, the present invention concerns a telescopic tube for electric household appliances equipped with means for conducting electricity along the said tube.
II. Related Art and Other Considerations
In the sector of electric household appliances such as vacuum cleaners, carpet beaters or the like it is advantageous to use telescopic tubes which increase the versatility thereof. Particularly advantageous are so-called “electrified telescopic tubes”, namely tubes comprising means for conducting electricity along the said tube. These may be used, for example, in a vacuum cleaner where it is required to position the ON/OFF button on the handle of the appliance or in order to prevent the electric power supply cable from interfering with the suction nozzle (also called “brush”).
In the description below, “closed configuration” will be understood as meaning the configuration where the telescopic tube assumes a minimum length, while “extended configuration” is understood as meaning the configuration where the telescopic tube is at least partially extended telescopically. In particular, in the “completely extended configuration” the tube assumes its maximum length.
Electrified telescopic tubes are already known in the art. DE 195 35 493 describes an electrified telescopic tube for a vacuum cleaner, comprising an extendable suction duct to which a cabling duct housing an electric cable is connected by means of suitable fixing rings. Inside the cabling duct there is a movable pulley system with springs; the pulley may perform axial translatory movements inside the cabling duct. The cable is wound around the pulley and forms an extra bend inside the cabling duct. In this way, when the vacuum cleaner tube is extended, the electric cable inside the cabling duct is unwound at least partially. The cable is kept tensioned by the recall force of the springs. When the tube is again brought into the closed configuration, the action of the recall force of the springs allows the original configuration of the cable and the pulley to be restored and at the same time the cable to be kept tensioned.
The solution of DE 195 35 493 involves certain disadvantages: the presence of the pulley system inside the cabling duct results in excessively large dimensions of the said duct and consequently the electrified telescopic tube. For this reason, this type of tube is not very easy to handle and therefore unsuitable for use in electric household appliances. Moreover, so that the cable may be housed inside the cabling duct and wound around the pulley, it must be bent inside the cabling duct; these bent sections result in wear of the cable—in particular its insulating coating—and therefore with time may give rise to dangerous short-circuits.
Moreover this known electrified tube has a complicated structure and requires assembly which is long and costly.
EP 0,848,926 B1 discloses a second type of electrified telescopic tube for a vacuum cleaner. This tube is formed by an outer suction tube, an inner suction tube which is partially slidable inside the outer suction tube, an outer cabling duct and an inner cabling duct which is partially slidable inside the outer cabling duct. The cabling ducts, which are partially inserted one inside the other, contain an electric cable; moreover they are arranged outside the inner suction tube and inside the outer suction tube. The electric cable has a linear length greater than the length of the tube in the extended configuration and, so as to be able to assist the telescopic extension thereof, is wound helically inside the cabling ducts.
The solution of EP 0.848,926 B1 is also disadvantageous in terms of overall dimensions of the tube: helical winding of the electric cable in fact requires the cabling duct having dimensions such as to prevent excessive bending of the cable, in order to prevent problems of wear thereof which may result in dangerous short-circuits. Moreover, in this type of electrified telescopic tube, the outer suction tube surrounds both the inner suction tube and both the cabling ducts. In order to reduce the cross-sectional dimension of the outer suction tube, ducts and tubes with an irregularly shaped cross-section are used, these being difficult and costly to produce.
EP 0 835 632 A discloses an adjustable electrical connection device for telescopic vacuum cleaner hose. The arrangement comprises at least two hollow tube parts which are inserted into each other and mechanically coupled to sections of the telescopic tube. The tube parts include electric connector devices at ends which oppose each other. The electric connectors are connected to each other over an electric conductor which is arranged in the interior of the tube parts. A section of the electric conductor in the interior of the tube part which is stationary with respect to the other tube part, is arranged as a coil. Elastic clamp parts are preferably formed in the tube part with the coiled conductor to prevent tensions on the conductor, whereby one clamp part is arranged at the end of the connector, and the other end is arranged at the end of the moving tube part, where the conductor is inserted.
The arrangement according to EP 0 835 632 is disadvantageous as it is not safe, it is rather complicated to be assembled and bulky.
EP 0 738 492 A describes several embodiments of extension pipes for electric vacuum cleaners. The extension pipes comprise a first and a second casings housing a flexible conductor connecting two terminals.
DE 197 31 559 A discloses a vacuum cleaner. The vacuum cleaner has in the suction nozzle a third wire and a rotating brush driven by a motor. The suction nozzle and a connecting piece of the handgrip are joined by an extension piece which is hollow, through which the dust-containing air flows and which is connected with one wire of the suction hose. The length of the extension piece can be altered in controlled fashion. The extension piece has a first bit with a first wire introduced first of all into the connecting piece of the handgrip and a second bit in which a third wire is introduced and which is designed so that its length can be altered with the first bit.
U.S. Pat. No. 3,534,317 discloses a system and apparatus for electrically connecting a vacuum cleaner and a remote motor driven brush tool.
DE 44 04 394 A discloses an adjustable electrical connection device for telescopic vacuum cleaner hose The arrangement comprises at least two hollow tube parts which are inserted into each other and mechanically coupled to sections of the telescopic tube. The tube parts include electric connector devices at ends which oppose each other. The electric connectors are connected to each other over an electric conductor which is arranged in the interior of the tube parts. A section of the electric conductor in the interior of the tube part which is stationary w.r.t. to the other tube part, is arranged as a coil. Elastic clamp parts are pref. formed in the tube part with the coiled conductor to prevent tensions on the conductor, whereby one clamp part is arranged at the end of the connector, and the other end is arranged at the end of the moving tube part, where the conductor is inserted.